GMR is a quantum mechanical magnetoresistance effect observed in thin-film structures composed of adjacent ferromagnetic and non-magnetic conductive layers. Magnetization of the adjacent ferromagnetic layers causes a change in the electrical resistivity of the GMR structure. The magnetization direction can be controlled by applying an external magnetic field to the GMR structure. Electric current can flow through the magnetic super lattice of the GMR structure using two different geometries. In a current-in-plane (CIP) geometry, the current flows in the plane of the layers. In a current-perpendicular-to-plane (CPP) configuration, the current flows perpendicular to the plane of the layers.
Modern mobile devices (e.g., smart phones) often include an electronic compass to determine a user's direction of travel. Some conventional electronic compasses use CIP-GMR sensors to sense external magnetic fields. Because CIP-GMR sensors have a maximum GMR effect of about 15%, the dynamic range, sensitivity and signal-to-noise ratio (SNR) of CIP-GMR sensors may be too low for some electronic compass applications.